Pearl is one of the most miraculous creations of nature. This lustrous hard and valuable object is produced by live shelled mollusks such as marine or freshwater oysters, clams, and mussels (bivalves). The formation of pearl is a defensive mechanism that can be seen in these types of creatures.
The ability of pearl creation can be seen in both freshwater and saltwater bivalves. Freshwater bivalves such as mussels belong to the family unionide and saltwater bivalves such as pearl oysters belong to the family pteriidae. Other than freshwater bivalves, pearls are also formed within freshwater clams belonging to the family unionoida.
Process of pearl formation
The process starts with entering of a foreign body like a parasite into the shell of the creature. This process may also start with the entering of any other organic material that acts as a foreign body.
The body of these mollusks is composed of two regions. They are the outer shell and the soft body tissue called the mantle. When the mantle gets attacked by foreign bodies or a parasite, a protective layer is made by the mantle.
This protective layer is formed by the deposition of nacre which has a specific chemical composition.
Nacre can be made with calcium carbonate in the form of the mineral aragonite. Nacre can be sometimes made by a mixture of aragonite and calcite (together called conchiolin).
Nacre is known as the mother of Pearl. It protects the mantle from irritation and injury.
The protective layer created around the foreign body is known as the pearl sac. The pearl sac is created by the nacre. The pearl sac becomes harder with time and as the final result, the pearl is made.
The below picture shows a shell of mussel.
The below picture is a shell of an oyster.
Natural pearls and cultured pearls
Pearls can be found in natural ways and cultured in pearl farms. Natural pearls and cultured pearls are different from each other.
Natural peals are called wild pearls. They are rarely found in nature. These pearls consist of 100% calcium carbonate and conchiolin. Pearls that are created naturally comes in perfectly round shapes.
Cultured pearls are formed in pearl farms. Several methods are used to get pearls available within a short period. The value of cultured pearls is lower than natural pearls. The most popular method of farming pearls is to create an irritant from a piece of mantle epithelium called a graft, of a donor shell.
Pearl farming is one of the major occupations in some countries such as Tahiti, China, Australia.
Value of a pearl
Natural pearls are very rare jewels with fine quality. The value of a pearl is determined by its size, color, luster, shape, quality of surface, and orientation. Gemological X-ray equipment and microscopes are commonly used to distinguish natural pearls from cultured pearls by observing their growth rings.
Jewelry with pearls is sold with a higher value like jewelry with gems and diamonds. Jewelry with natural pearls is usually more expensive than cultured pearls.
Edible oysters and edible mussels sometimes produce pearls but they are valueless and not very durable.
The most common types of cultured pearls are Keshi pearls and Tahitian pearls. Tahitian pearls are black in color and highly valuable. These black pearls are found in black pearl oysters but they produce them rarely in a natural way. Most Keshi pearls are small and irregular in shapes and the value is usually lower than the black pearls.
Other than culture, pearls can be harvested by hunting. Pearl hunting affects the diversity and natural processes in the ocean bed and the rivers. All mussels and oysters are not capable of making pearls. Divers pull a large number of creatures but perfect pearls are found only in a few oysters. Just for the few pearls, large numbers of these amazing creatures are killed by the man in the pearl hunt. Humankind needs to be responsible and sensitive to the environment. Each and every organism is important for the balance and survival of such an ecosystem.